Laboratory Studies of Peroxy Radical Reactions of Importance for Tropospheric Chemistry

Summary

Studies of the UV absorption spectra as well as the kinetics and products of reactions of the following organic peroxy radicals have been carried out: CH₃O₂, CH₂=CHCH₂O₂, HOCH₂CH₂O₂, CH₃CH(OH)CH(O₂)CH₃, (CH₃)₂C(OH)CH₂O₂, (CH₃)₂CH(OH)CH(O₂)(CH₃)₂, CH₃OCH₂O₂, CH₃C(O)CH₂O₂ and C₂H₅C(O)O₂. These radicals were chosen to be representative of those formed from the degradation of some classes of volatile organic compound (VOC) likely to be important in tropospheric chemistry (i.e. alkanes, alkenes, conjugated dienes, alcohols, ethers, aldehydes and ketones). Kinetic studies of the self reactions and reactions with HO₂ were carried out using the molecular modulation technique and the laser flash photolysis technique, coupled with UV absorption spectroscopy. Product studies were carried out by long pathlength Fourier transform infra-red spectroscopy and UV-visible diode array spectroscopy. This work has also allowed investigation of a variety of laboratory sources of peroxy radicals.

The results have been used, along with those obtained by other LACTOZ participants, to establish trends of reactivity of peroxy radicals, and to assign rate coefficients to complex peroxy radicals, in particular those formed from the OH-initiated degradation of isoprene. A degradation mechanism of isoprene to first generation products has been assembled, incorporating these data, which gives a good description of the product yields measured in other laboratory studies.